Photolithography tools are used to expose an image of a pattern formed on a mask onto a silicon substrate. Currently known photolithography tools include step-and-repeat type ones and step-and-scan type ones. A crucial factor for evaluating the performance of a photolithography tool is accuracy, namely the accuracy of the movement of relative components of the photolithography tool during an exposure process. The relative components that need to be moved include a reticle stage for holding the reticle and a wafer stage for supporting the silicon wafer. In a general case, a standard proportional-integral-derivative (PIM-based control system is employed to control the motion of the components based on positional feedbacks. Moreover, in order to achieve nano-level positioning accuracy and rapid response, the components of the photolithography tool is required to have a high acceleration and deliver a small shock to a measurement reference frame. As the two requirements conflict with each other, many photolithography tools adopt a structure consisting of the wafer stage and a balancing mass, wherein a motor coupled to the wafer stage generates a high acceleration to Meet the requirement for rapid response and the balancing mass absorbs, upon receipt of a reaction force from the motor, the shock from the wafer stage by moving backward to meet the requirement for a small shock to the measurement reference frame. The above wafer stage-balancing mass structure follows the law of conservation of motion of centroid during its movement. In practical applications, the motor drives the wafer stage by applying force on the centroid, i.e. center of mass, of the wafer stage while the position of the wafer stage is measured with respect to a midpoint, i.e. center of form, of the wafer stage. Therefore, it is needed in the position control to shift the control signal from the midpoint to the centroid. The shift has close relationship with the deviation between the midpoint and the centroid, and if the positions of the midpoint and the centroid are not correctly calibrated and leaving a large deviation therebetween, the control performance will not achieve the desired accuracy. Moreover, the large deviation may further cause over-exertion of the motor and excessive heat and high power consumption. Therefore, accurate calibration of the centroid of the wafer stage is required for achieving a good performance of the photolithography tool.